I have had a Mark I for many years and it has always been reliable. I have not found any ammo that it will not shoot. I bought my son a Mark III last year for his birthday. I figured I would stay with the Mark series since I had such good luck with mine. Worst pistol I have every bought. I never found any ammuntion that it would shoot consistently. The mags. were hard to seat into the well. This caused feeding problems. It was very rare to run an entire mag of ammunition without a hang up. You could pull the trigger and it not fire and pull it down think you had another jam and all of a sudden with no pressure on the trigger it would go off. Never saw anything like it.
One good thing about the Mark III is that it did teach my 15 year old son very good gun safety due to all the problems with it. Sold that pistol and will never by another Mark III.